Preparation of Ca-β″-Al_2O_3 from Alumina Gel

摘要

Using aluminium nitrate solution containing calcium and magnesium cations, and saturated ammonium oxalate solution in concentrated ammonium hydroxide as precipitating agent, alumina gel was prepared. The gel was calcined at different heating rates up to 400℃ and then at different temperatures and soaking times. The calcination products successively appeared as aluminium oxides, calcium aluminate and calcium-beta″-alumina. The obtained calcium-beta″-alumina crystallites were plate-shaped and the direction perpendicular to the crystallite surface was parallel to the Z-axis. It was found that the kinetics of calcium-beta″-alumina synthesis depends on the presence of a molten salt during the gel thermal treatment. The mechanism of calcium-beta″-alumina formation is proposed as a reaction between formerly produced calcium aluminate and aluminium oxide of the alpha form. Sintered bodies prepared from the calcium-beta″-alumina powder were characterized by good ionic conductivity.